TITLE: GCN CIRCULAR NUMBER: 45988 SUBJECT: GRB 261017A: Possible Swift/UVOT Detection DATE: 26/10/19 13:42:13 GMT FROM: Paul Kuin at MSSL N.P.M. Kuin, A.A. Breeveld, M.J. Page (MSSL/UCL) and M. H. Siegel (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 261017A 90 s after the BAT trigger (Siegel et al., GCN Circ. 45974). A source consistent with the XRT position (Beardmore et al.,GCN Circ. 45977) is detected in the initial UVOT exposures. Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 90 1377 373 20.41 +/- 0.24 v 631 1427 97 >18.6 b 557 5666 198 >19.2 u 302 5538 501 >19.2 w1 680 1304 78 >18.5 The source varies between exposures, is sometimes absent, and appears double in two images. It might not be a point source. The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.023 in the direction of the burst (Schlegel et al. 1998).